Will my 60-day tourist visa allow me to stay in Thailand for 109 days without issues?

I don't know what the O/P is referring to when they ask "do you think I'll be okay" <- I mean okay when they stamp into the country (I'd have the proof of funds, proof of onward travel and proof of hotel), okay when getting their extension (depending on the office they might need a TM.30 receipt to get one).

If he has an extensive history of living here on visa exempt or tourist visa entries I'd say he should be prepared to be questioned at passport control. Otherwise his plan sounds doable.

Paul, I am hoping one of the admins will reply to your post because I am not one of the experts. I am not sure Lance understands your situation properly. It does not matter if you are married to a Thai, if you enter on a SETV not a Non-O based on marriage surely that SETV that you enter on is the only thing that can be extended and that only once for 30 days. You would need to do a border bounce to get a 30 visa exempt entry before the end of your extension. If it is not too late, you could consider a METV. It does sound like you wish to go down the Non-O based on marriage route, but that would also be an option

No problem. You have a visa so you don't need onwards flights. Just have 20k handy and all your marriage documents for 60 day extension.